Radio Frequency (RF) sputtering is a technique which is well known and described well in the literature (B. Chapman, "Glow Discharge Process", J. Wiley and Sons, NY, 1980, p 135-173). It is a type of diode sputtering with a cathode electrode, an effective anode, and a plasma within a vacuum chamber. The electrodes are typically driven at high voltage (1000-1500 volts) and high frequency (13.56 megahertz). The plasma is formed by the high voltage induced breakdown of the gas in the chamber, and typically assumes a plasma potential near ground, which is the potential of the chamber walls. The cathode electrode is bombarded at high energy by ions in the plasma during the "negative" portion of the applied voltage and by electrons during the "positive" part. Thus, no net charge flows through the cathode electrode. The cathode electrode is sputtered by the high energy ion bombardment. This sputtering is used either for erosion of samples on the cathode surface, or net deposition on samples placed on an opposing surface with suitable support.
Reactive Ion Etching is a technique which adds a chemical reaction to this ion bombardment process. Certain gases, such as freon, oxygen, silane, etc., are chemically active with a number of common materials used in device fabrication (silicon, quartz, polyimide, etc.). When used in an RF sputtering system, these reactive gases cause additional etching of the surface (over sputtering alone) by chemically combining with surface atoms and forming a volatile species which leaves the surface and can be pumped away. Typically, the operating pressure and gas flow rate would be higher in a reactive ion etching device as compared to a simple RF device alone, but the underlying operation of the plasma would be similar and dominated by the RF applied voltages.
Recently, a related device has been developed (C. Horwitz, Applied. Physics. Letter, Vol. 43, 1983, p 977), which used a hollow cathode glow to enhance the plasma in the RF plasma. This device was characterized under similar operating conditions to a regular RF device, and produced higher etch rates. The herein disclosed invention, although similar in structure, constitutes a distinct improvement over the Horwitz device and has a number of operating advantages, which will be described later.